1. Field
Example embodiments relate to a semiconductor device. More particularly, example embodiments relate to an analog to digital converting device, an image pick-up device capable of canceling noise, and a signal processing method of the image pick-up device.
2. Description of the Related Art
An image pick-up device is a semiconductor device converting an optical image to an electric signal. Generally, image pick-up devices using a charge coupled device (CCD) or a complimentary metal oxide semiconductor (CMOS) image sensor (CIS) have been widely employed.
Using a CIS is economical compared to using a CCD, since a CIS may be made using general CMOS processes and may be integrated with an analog to digital converter (ADC) on a chip. In addition, as a CIS may be designed to operate using low-power and low-voltages, CIS devices are widely used in portable devices, e.g., mobile phones, digital cameras, and so forth.
A CIS, different from a CCD, requires conversion of an analog signal output from an active pixel sensor (APS) array into a digital signal. A high resolution analog to digital converter (ADC) is used in a CIS for such conversion. The CIS may be divided into a single ADC method and a column ADC method according to how the ADC is embodied. A single ADC method converts APS analog output signals output from all columns into digital signals within a predetermined time using one ADC operating at high speed. The single ADC method may provide a reduced CIS chip size. However, due to such high speed operation, the single ADC method consumes a large amount of power.
On the other hand, the column ADC method includes arranging a simple ADC circuit for each column. The column ADC method provides lower power consumption, but has a large CIS chip size. The column ADC method performs correlated double sampling (CDS) on an analog output voltage, e.g., a pixel output signal, stores a voltage corresponding to a performance result, compares a voltage generated in CDS operation with a predetermined reference voltage in response to a ramp signal generated by a ramp signal generator, and outputs a comparison signal from which a digital signal is generated.
Recently, as a demand for high resolution images increases, many companies are developing CIS devices having high resolution. Such high resolution CIS devices include smaller pixels. In this case, image deterioration by power supply noise output from a pixel becomes a big issue and a technique to cancel such image deterioration is greatly needed.
A differential comparator of a CDS circuit used in a conventional column ADC method has good noise property for power supply noise generated by a CDS block itself and for coupling noise due to switching. However, it does not efficiently cope with power supply noise generated by a pixel outside of a CDS block.